The present invention relates to shielding of radiating radio frequency electromagnetic emissions and more particularly to shielding a source of such emissions so as to protect from excessive, prolonged exposure to such emissions any people and objects that might be injured or damaged by such exposure, while still facilitating the efficient and unobstructed emission from the source, for its intended purpose.
Shields for shielding people and objects from radio frequency electromagnetic emissions have long been known and have a number of uses. In recent years there has been a very significant increase in the use of mobile telephones and paging devices. As their use has increased, more communications towers have been built for radio frequency transmissions for communication devices, such as mobile telephones, pagers and the like. Also, it has become increasingly common for radio frequency communications of this type to be transmitted from antennae located on and in buildings and at other locations close to large numbers of people, both inside and outside of the building. The increased amount of transmission near concentrations of people has led to an increased need for a simple, economical, and compact shield to protect people and the environment from stray radio frequency emissions.
Accordingly, there is a need to provide a shield for electromagnetic radio frequency emissions, which is simple, economical, and compact, and which is an efficient means for protecting people and the environment from radio frequency emissions from communications antennae transmitting to mobile telephones and pagers.
There is also a need to provide shielding of a radio frequency antenna for environmental protection while minimizing the reflective or refractive transmission of radio frequency energy around the radio frequency shielding.
There is an additional need to provide or permit physical access to a radio frequency antenna without providing an escape path for radio frequency energy through shielding provided for the antenna.
There is a further need to minimize visibility and visual obviousness of a radio frequency antenna and its shielding.
The present invention involves placing a layer of radio frequency-energy-reflecting material between an antenna and people or objects near the antenna, that might be harmed by prolonged exposure to excessive amounts of radio frequency electromagnetic energy. A layer of radio frequency-energy-absorbing material is then placed between the reflecting material and the antenna, thereby absorbing a portion of the emitted energy that would otherwise pass to people or energy-sensitive objects near the antenna. The reflective layer then reflects energy that passes through the absorbing layer, further preventing the radio frequency energy from reaching people or energy-sensitive objects. The energy that is reflected by the reflective layer again passes through the absorbing layer, where another portion of the energy is absorbed. In this way, only a tiny portion of the original magnitude of transmitted energy finds its way back to the antenna and thus minimizes the amount of reflected back-scatter that might otherwise mix with and thus distort the transmission patterns of the signals issuing from the antenna.
In another aspect of the present invention, an absorbing layer is placed between the combination absorbing and reflective layers and a radio frequency-energy transmitting or transparent layer through which the radio frequency energy is intended to be transmitted.